1. Field of the Invention
Aspects of the present invention relate to a fusing unit and an image forming apparatus having the same including a plurality of pressing rollers to fuse an image transferred to a printable medium.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus scans a light onto a photosensitive medium charged to have a predetermined electric potential to form an electrostatic latent image, develops the electrostatic latent image with a predetermined color, and transfers and fuses the developed image onto a printable medium to print an image. A fusing unit is provided along a printing path of the image forming apparatus. The fusing unit fuses a developer image transferred to the printable medium onto the printable medium.
The fusing unit includes a heating roller and a pressing roller with the printable medium interposed therebetween. The heating roller applies heat to the printable medium. The pressing roller applies pressure to the printable medium to fuse the developer onto the printable medium. Fusing units generally employ a plurality of pressing rollers to widen a nip area between the heating roller and the pressing roller where the developer image is fused onto the printable medium to improve fusing efficiency.
FIG. 1 is a schematic view illustrating a configuration of a conventional fusing unit 10 employing a plurality of pressing rollers. The conventional fusing unit 10 includes a heating roller 20 applying heat to the printable medium M, and a first pressing roller 30 and a second pressing roller 40 facing the heating roller 20. The first pressing roller 30 and the second pressing roller 40 rotate passively by means of a friction force generated by the rotation of the heating roller 20. Accordingly, the first pressing roller 30 and the second pressing roller 40 rotate with the same speed as the heating roller 20.
In the conventional fusing unit 10, before the printable medium M passing the first pressing roller 30 enters the nip between the second pressing roller 40 and the heating roller 20, the printable medium M is separated from the heating roller 20 to generate a detached area A. Since the printable medium M is apt to proceed in a tangential direction to the heating roller 20 after passing the first pressing roller 30, the printable medium M does not remain in contact with the heating roller until the leading edge of the printable medium M passes between the second pressing roller 40 and the heating roller 20.
Since a developer image T on the area A of the printable medium M that is separated from the heating roller 20 does not have a sufficient fusing time, the developer image T may separate from the printable medium M. As a result, a spot is generated in an image formed on the printable medium M, and printing quality deteriorates.
The separation of the developer image, and the spot generated by the separation of the developer image, may be aggravated in the case of a color image forming apparatus using a plurality of developer units for color image forming operations.